JP2009000601A - Magnetic separator and carrier for electrophotography magnetically-separated by the magnetic separator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic separator which is capable of conducting the precise separation not only in case where a powder material including a magnetic material and non-magnetic material of which the magnetic characteristics has a big difference but also in case where a powder material including a strong magnetic material and a weak magnetic material of which the magnetic characteristics has not a big difference, and in case where the separation is conducted by means of the threshold value. <P>SOLUTION: In the magnetic separator having at least a hollow cylindrical tube comprised of a non-magnetic material, a magnetic pole generating member arranged in the hollow cylindrical tube, a driving part to rotate the hollow cylindrical tube, a holding part to fix and hold the magnetic pole generating member, a supply part to supply the powder material to the surface of the hollow cylindrical tube and a recovery part to recover the powder material, it is characterized in that a plurality of hollow cylindrical tubes are equipped and arranged so that the hollow cylindrical tubes are in proximity and neighbored with each other, and in that the powder material is transferred between the hollow cylindrical tubes arranged in proximity to reach the recovery part. It is preferable that the powder material is transferred with vibration. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a magnetic separator equipped with a rotating roller for accurately separating the magnetic strength of a powdery substance, and in particular, a small amount of weakly magnetic or nonmagnetic powdery substance from a large amount of ferromagnetic powdery substance precisely. The present invention relates to a magnetic separator to be separated and an electrophotographic carrier magnetically selected by the magnetic separator.

  A magnetic separator is a case where defective products that cause deterioration in the purity of raw materials or products are mixed in non-defective products such as raw materials and products handled in the manufacturing process of powdered substances in various industrial fields. In addition, the non-defective product and the defective product are separated using the presence or absence of magnetism between the non-defective product and the defective product, or the difference in strength. Such separation methods are not only for magnetic powders such as metal powders, which are currently handled as raw materials and products in various industrial fields, but also for the distribution of precise magnetic properties, especially for electrophotographic carriers. This is also done for the required objects.

  In general, in the magnetic separation process using a magnetic separator, if there is a clear difference between the non-defective product and the non-defective product in terms of magnetic properties such as the presence or absence of magnetism, a mixture of good and defective products These can be easily separated by using a magnet for the product.

However, a problem arises when the difference between the magnetic properties of the non-defective product and the defective product is not large, such as a ferromagnetic material and a weak magnetic material, or when the magnetic properties are separated at a certain threshold. For example, when the external magnetic field is 1000 [Oe], the magnetization of the ferromagnetic material is 70 [Am ² / kg], and the magnetization of the weak magnetic material is 40.
[Am ² / kg] It is difficult to remove only the latter weak magnetic material from a powdery substance in which these are uniformly mixed. In addition, for a powdery substance having a continuous magnetization from 40 to 70 [Am ² / kg], only particles having a magnetization of 55 [Am ² / kg] or less are removed. When separation is performed with a magnetic threshold, it is difficult to accurately separate these non-defective products and defective products. Furthermore, it has been extremely difficult to accurately separate a weak magnetic substance contained in a small amount from a powdery substance containing a large amount of ferromagnetic substance.

  The reason is that the ferromagnetic material and the weak magnetic material are always mixed, and the weak magnetic material is entrained in the ferromagnetic material. This is because the weak magnetic material itself has magnetism and is attracted to the magnet, and as a result, it is difficult to be discharged outside.

  In addition, when the magnetic material is brought into contact with the magnet, the magnetic material can follow the magnetic field of the magnet (hereinafter referred to as “magnetic ear”), but when a weak magnetic material exists in the middle of the magnetic material, the magnetic separation drum is used. When the magnetic material is separated from the weak magnetic material portion of the magnetic spike by the centrifugal force generated by the rotation of the member, the ferromagnetic material existing at the tip of the magnetic material is discharged, and as a result, the separation accuracy is significantly lowered.

  To give a concrete example, the magnetic separators disclosed in Patent Documents 1 and 2 are basically composed of a non-magnetic material as a main component, and the non-magnetic material is mostly composed of a powdery substance. It is a means for separating and removing a magnetic substance contained in a small amount. In such applications, it is effective for high-precision separation, but since there is no mechanism for separating and removing non-magnetic materials and collecting magnetic materials in the first place, magnetic materials occupy most of them, and a small amount is contained in them. It is unsuitable for the usage of separating and removing nonmagnetic materials.

In the magnetic separator disclosed in Patent Document 3, the magnetic material occupies most of the powdered material containing a small amount of the non-magnetic material, and the non-magnetic material is separated and removed to recover only the magnetic material. It has a mechanism. However, since there is only one hollow drum that performs magnetic separation processing, for example, it is made of a magnetic material, and a certain magnetic material is used for a powdery material in which materials having various magnetic strengths are mixed. When performing magnetic separation such as removing only components lower than the threshold value, the substance having low magnetism to be separated / removed itself is attracted to the surface of the hollow drum by magnetism, so that separation with high accuracy cannot be performed. In order to separate, it is necessary to take measures such as increasing the number of revolutions of the hollow drum or lowering the magnetic flux density, and as a result, the highly magnetic components to be recovered are also removed, resulting in a decrease in separation accuracy. In addition, there is a problem that the yield is reduced.
JP 2006-116453 A Japanese Patent No. 2932880 JP-A-11-309383

  The object of the present invention is to solve the above-mentioned problems of the conventional magnetic separator, not only when there is a clear large difference in magnetic properties, such as a magnetic material and a non-magnetic material, but also a ferromagnetic material and a weak magnetic material. Thus, it is an object of the present invention to provide a magnetic separator that accurately separates even when the difference in magnetic characteristics is not large or when separation is performed at a certain threshold. Furthermore, this magnetic separator is to efficiently produce an electrophotographic carrier that does not contain a weak magnetic material.

In order to achieve the above object, the present invention has the following configuration.
(1) A magnetic separator according to the present invention fixes a hollow cylindrical body made of at least a nonmagnetic material, a magnetic pole generating member disposed inside the hollow cylindrical body, a drive unit for rotating the hollow cylindrical body, and a magnetic pole generating member A holding unit for holding, a supply unit for supplying a powdery substance to the surface of the hollow cylindrical body, and a recovery unit for recovering the powdered substance, comprising a plurality of the hollow cylindrical bodies, and these hollow cylindrical bodies It is characterized by being arranged adjacent to each other.

  The magnetic pole generating member disposed inside the hollow cylindrical body may be of any type as long as it can generate a magnetic pole. For example, if a permanent magnet is used, there is an advantage that the mechanism of the magnetic separator becomes simple. On the other hand, if an electromagnet is used, there is an advantage that the magnetic flux density can be arbitrarily adjusted in accordance with the magnetic property value of the powdery substance subjected to magnetic separation.

  By fixing the magnetic pole generating member by the holding portion and rotating the hollow cylindrical body, the powdery substance passes over the magnetic field formed on the surface of the hollow cylindrical body formed by the magnetic pole generating member. The surface of the hollow cylinder has a plurality of magnetic poles in the circumferential direction. At the center of the magnetic pole, a magnetic spike is formed by a powdery substance, but when the position shifts from the center of the magnetic pole, the magnetic spike lies down sideways, and when it moves to the next magnetic pole, the magnetic spike is formed again. This is repeated while the hollow cylinder rotates once, and the ferromagnetic material, the weak magnetic material, and the nonmagnetic material in the powdery substance are replaced. Furthermore, it is preferable to always vibrate the powdery substance while the powdery substance supplied to the surface of the hollow cylinder moves on the surface of the hollow cylinder. By oscillating the powdery substance, the ferromagnetic substance, the weak magnetic substance, and the nonmagnetic substance in the powdery substance are replaced more frequently.

By installing a plurality of hollow cylinders close to each other as in the present invention and adjusting the position and magnetic flux density of the magnetic pole generating member installed inside each hollow cylinder, a plurality of ferromagnetic bodies in the powdery substance can be obtained. The weak magnetic material contained in the powdery substance cannot move between the hollow cylinders, but remains on the surface of one intermediate cylinder, or a non-magnetic material. In the same manner as above, the centrifugal force generated by the rotation of the hollow cylindrical body is discharged to the outside of the magnetic separator. In the present invention, accurate magnetic selection can be achieved by transferring the ferromagnetic material between the hollow cylinders.
(2) In the movement path of the powdery substance, it is preferable to have at least one proximity part where the powdery substance rises from the hollow cylinder located below to the hollow cylinder located above. It is more preferable that it goes up from the bottom to the top. This makes it possible to perform more accurate separation by utilizing the drop of weak magnetic material or non-magnetic material due to gravity.

(3) B1 [T1] is the magnetic flux density formed by the magnetic pole generating member of the hollow cylindrical body located upstream of the moving path of the powdery substance in the proximity of the hollow cylindrical bodies, and the moving path of the powdered substance When the magnetic flux density formed by the magnetic pole generating member in the hollow cylindrical body located on the downstream side is B2 [T], it is preferable that the condition of 0 ≦ Log (B2 / B1) ≦ 5 is satisfied, and 0.5 ≦ Log It is particularly preferable that the condition (B2 / B1) ≦ 2 is satisfied.
Here, when the numerical value exceeds 5 in the above condition of the magnetic flux density, it is formed on the surface of the hollow cylindrical body located on the downstream side with respect to the magnetic field formed on the surface of the hollow cylindrical body located on the upstream side. The magnetic field becomes excessively strong, and the weak magnetic material to be removed also moves to the hollow cylindrical body located on the downstream side, which may significantly reduce the magnetic separation accuracy.
(4) While the powdery substance supplied to the surface of the hollow cylinder is moving on the surface of the hollow cylinder, the powdery substance is vibrated, thereby enabling more accurate separation. As described above, the ferromagnetic material and the weak magnetic material are always mixed. If the weak magnetic material is wound in the ferromagnetic material, the weak magnetic material is weakened by the attractive force of the ferromagnetic material to the magnet. The body is also constrained to the magnet side and is not discharged to the outside of the magnetic separator, and is moved together with the ferromagnetic body to the next hollow cylindrical body, so that the separation accuracy is significantly reduced. Therefore, by always vibrating the powdery substance, the ferromagnetic substance, the weak magnetic substance, and the nonmagnetic substance in the powdery substance are frequently exchanged, and accurate separation becomes possible.

As a means for giving vibration to the powdery substance, for example, a means for vibrating the hollow cylindrical body 2 by the vibrator (16) shown in FIG. The means for vibrating the hollow cylinder is a direct means for vibrating the powdery substance. Further, means for blowing gas to the powdered substance by the gas nozzle (17) shown in FIG. ) To apply an AC voltage between the hollow cylindrical body (2) and the counter electrode plate (21). As means for blowing the gas, the gas pressure may be constant or a pulse pressure. As a means for applying an AC voltage to the hollow cylinder, an electrode plate or the like is installed so as to face and face the hollow cylinder, and an AC voltage is applied between the hollow cylinder 2 and the electrode plate. At this time, the Coulomb force acts on the powdery substance due to the minute charge generated on the surface of the powdery substance due to the stirring action by the rotation of the hollow cylindrical body or the charge induced to the powdery substance by the applied electric field, and the powdery substance becomes hollow. The powdery substance vibrates actively by moving between the cylindrical body and the electrode plate and increasing the frequency of the applied voltage.
(5) The interval between the adjacent portions of the plurality of hollow cylindrical bodies is preferably in the range of 3 mm to 50 mm, and more preferably in the range of 10 mm to 20 mm. If the interval is too narrow, weak magnetic bodies and non-magnetic bodies also easily move between the hollow cylindrical bodies. On the other hand, if the distance is too wide, the ferromagnetic material cannot move between the hollow cylinders.

(6) It is preferable that at least a part of the surface of the hollow cylindrical body has an uneven shape. As an example, a shape in which a mesh-shaped recess (20) is provided on the surface of a hollow cylindrical body (2) as shown in FIG. By increasing the conveying power of the powdery substance with the irregular shape of the surface, the movement of the powdery substance on the surface of the hollow cylindrical body is activated, and the ferromagnetic substance, weak magnetic substance and nonmagnetic substance in the powdery substance are replaced. Is performed frequently, and more accurate separation becomes possible.
(7) While the powdery substance supplied to the surface of the hollow cylinder is moving on the surface of the hollow cylinder, the rotation of each hollow cylinder is switched in two directions, clockwise and counterclockwise. Separation with high accuracy is possible. As described above, the surface of the hollow cylindrical body has a plurality of magnetic poles in the circumferential direction, and a magnetic spike is formed by a powdery substance at the center of the magnetic pole. When moving to the next magnetic pole, the magnetic spike is formed again, and this process is repeated while the hollow cylinder rotates once, and the ferromagnetic material, weak magnetic material and nonmagnetic material in the powdery substance are Replacement is frequent. At this time, by switching the clockwise and counterclockwise directions, the surface movement distance of the powdery substance per hollow cylinder is extended and the number of times of replacement increases, and the weak magnetic material and the non-magnetic material are separated to the outside of the magnetic separator. Emissions are promoted.

(8) The average value of the number of rotations of each of the plurality of hollow cylinders is R [rpm], the radius of the hollow cylinder is r [cm], and the supply speed of the powdery substance supplied to any surface of the hollow cylinder is When M [kg / h] is satisfied, the condition of 2 ≦ 1000 (M / 2πrR) ≦ 80 is preferably satisfied, and the condition of 4 ≦ 1000 (M / 2πrR) ≦ 20 is particularly preferable. Here, 2πrR represents the moving distance of the powdery substance on the surface of the hollow cylinder per unit time. When M / 2πrR is less than 2, the moving distance of the surface of the hollow cylindrical body of the powdery substance per unit time may be excessively longer than the supply speed of the powdery substance. As a result, the powdery substance is magnetized by the magnetic field formed on the surface of the hollow cylindrical body, which may cause a problem of adhering to the apparatus wall surface. In addition, when M / 2πrR exceeds 80, the supply speed of the powdery substance becomes excessively high with respect to the moving distance of the powdery substance per unit time on the surface of the hollow cylinder, and the magnetic separation accuracy may be significantly reduced. There is.
(9) The present invention is a magnetic separator that performs magnetic selection of an electrophotographic carrier by the means described in any one of (1) to (8) above.

(10) The present invention is a carrier particle for electrophotography magnetically selected using the magnetic separator described in (9) above.
In general, an electrophotographic carrier is obtained by forming a resin film on the surface of core material particles containing iron as a main component. Core material particles serving as the core of the carrier are generally finely pulverized into a powder. It is obtained by granulating a slurry made of a magnetic material and a binder resin, and then sintering in a firing step. At this time, the dispersion of the magnetic substance and resin component in the slurry is non-uniform, and the component ratio in the core particle is uneven, or there are structural defects such as vacancies in the core particle during the granulation to sintering process. When this occurs, core material particles having a magnetization lower than the desired magnetization are generated. Even in the case of core particles having a desired magnetization, the magnetization may be lower than a desired value due to structural breakage such as cracking or corner chipping in handling operations such as stirring and transportation by a mechanical device when forming a carrier. . When such a carrier having a magnetism lower than a desired value and having a so-called weak magnetic material as a nucleus is mixed in the carrier product, the magnetic force received from the magnetic roller used in the developing unit in the copier is increased. It is weak and the carrier made of a weak magnetic material scatters in the developing unit, leading to the occurrence of an abnormal image. Thus, in the final stage of the carrier manufacturing process, magnetic separation is performed, and the weak magnetic material that causes the abnormal image is removed, so that the image can be maintained in high quality.

  According to the magnetic separator according to the present invention, not only when there is a clear and large difference in magnetic characteristics such as a magnetic body and a non-magnetic body, but also the difference in magnetic characteristics is not as large as that of a ferromagnetic body and a weak magnetic body. Even in the case of separation with a certain threshold value, it is possible to perform magnetic separation with high accuracy and to provide a high-quality electrophotographic carrier that does not contain a weak magnetic material.

Hereinafter, the present invention will be described with reference to embodiments. In addition, these are only one aspect | mode of this invention, and do not limit the technical scope of this invention.
As one aspect of the magnetic separator according to the present invention, there are apparatuses as shown in FIGS. 1, 2, 3, and 4, for example.

1 is a conceptual side view of a magnetic separator, FIG. 2 is a conceptual front view of the magnetic separator, FIG. 3 is an enlarged view of a side surface of a hollow cylinder and a magnetic pole generating member provided in the magnetic separator, and FIG. 4 is a front view of the hollow cylinder. It is the enlarged view seen from. 1-4, (1) is a magnetic separator exterior, (2) is a hollow cylindrical body, (3) is a magnetic pole generating member, (4) is a shaft, (5) is a defective product collection unit, (6) is Powdered material charging hopper, (7) Powdered material charging tray, (8) Powdered material charging direction, (9) Powdered material recovery tray, (10) Powdered material recovery hopper , (11) is the discharge direction of the powdery substance, (12) is the rotation direction of the hollow cylinder, (13) is the proximity gap of the hollow cylinder, (14) is the holding part of the magnetic pole generating member, and (15) is hollow (16) is a vibrator, (17) is a gas nozzle, (18) is an AC voltage power source, (19) is ground, (20) is a mesh-shaped recess, and (21) is facing. It is an electrode plate.

  As shown in FIG. 1, the magnetic separator according to the present embodiment, in the magnetic separation process, throws the powdery substance from the feeding hopper (6) through the feeding tray (7) in the feeding direction (8), and forms the bottom hollow. A powdery substance is supplied to the cylindrical body (2). Due to the rotation (12) of the hollow cylinder, the powdery substance moves to the upper part of the hollow cylinder, and in the interval between adjacent parts between the hollow cylinders (hereinafter also referred to as “proximity gap”) (13), It is attracted by the magnetic field of the hollow cylinder located and moves to the upper hollow cylinder. By repeating these steps, the powdery substance that has reached the top of the magnetic separator is discharged in the discharge direction (11) through the recovery tray (9), recovered by the recovery hopper (10), and supplied to the next step. .

Next, the present invention will be described in more detail with reference to examples and comparative examples.
[experimental method]
In order to evaluate the magnetic separation accuracy of the magnetic separator, a carrier A, a carrier B, and a non-magnetic material C having different magnetism are used as powdery material samples. Here, the carrier A is a ferromagnetic material, and the carrier B is a weak magnetic material, and the magnetization in an external magnetic field of 1000 [Oe] is 70 [Am ² / kg] and 40 [Am ² / kg], respectively. Since the non-magnetic material C does not have magnetism, the magnetization is 0 [Am ² / kg]. First, carrier A and carrier B are mixed at a ratio of A: B = 7: 3, and carrier A and nonmagnetic material C are mixed at a ratio of A: C = 7: 3 to prepare mixed powders AB and AC, respectively. These are separately subjected to magnetic separation using a magnetic separator, and the work of separating and removing the carrier B and the non-magnetic material C from the mixed powders AB and AC, respectively, is performed. Then, the magnetizations of the mixed powders AB ′ and AC ′ subjected to the magnetic separation treatment are measured, and the magnetic separation classification accuracy D defined by the following equation is evaluated. If the carrier B and the non-magnetic material C mixed with the carrier A can be completely separated and removed from the carrier A, the magnetic separation accuracy is theoretically 100%. Therefore, the higher the magnetic separation accuracy, the more magnetic separation accuracy of the magnetic separator is. It will be expensive.
Magnetic classification accuracy D (%) = 100 × (Y−X) / (A−X)
(A: Magnetization of carrier A, X: Magnetization of mixed powder before magnetic selection, Y: Magnetization of mixed powder after magnetic selection)
For measurement of magnetization, a VSM measuring device was used, and the magnetization of the sample was measured by applying to an external magnetic field 1000 [Oe].

[Experimental conditions]
(Experimental conditions of Comparative Example 1)
As Comparative Example 1, a magnetic separation process was performed using a drum type magnetic separator. The drum type magnetic separator is one of the most widely used types in the industry. It is a magnetic separator with a highly versatile mechanism used in various fields such as mining, ceramics, chemistry, and food. is there. Powder AB and AC are supplied to the drum surface from the top of the drum, and the drum surface is rotated. A powder recovery unit was installed at a location located slightly downstream of the drum, and the falling magnetically treated powder was recovered. The weak magnetic material and the non-magnetic material are structured to fall to the defective product collection unit by gravity and the centrifugal force generated by the drum rotation before reaching just below the drum.

(Experimental conditions of Comparative Example 2)
The magnetic separator shown in FIG. 1, which is an example of the magnetic separator proposed in the present invention, is used in a structure in which only one hollow cylinder is left and the other hollow cylinders are removed, and the powder is not vibrated. A magnetic separation process was performed. This eliminates the feature that the powder moves in the proximity gap between the plurality of hollow cylinders proposed in the present invention and the feature that gives vibration to the powder, and this is a comparative experiment that more significantly represents the effect of the present invention. did. The structure is similar to the drum type magnetic separator of Comparative Example 1.

(Experimental conditions of Example 1)
1 is an example of a magnetic separator proposed in the present invention. The vibrator is installed at the bottom of the magnetic separator, with only two hollow cylinders remaining and the other hollow cylinders removed. The whole apparatus was vibrated to give vibration to the powder, and a magnetic separation process was performed. 4 is formed on the surface of the hollow cylindrical body, and the proximity gap and the like of the magnetic separation means are as shown in Table 1 below.
(Experimental conditions of Example 2)
The magnetic separator shown in FIG. 1, which is an example of the magnetic separator proposed in the present invention, has four hollow cylinders and vibrates the vibrator installed at the bottom of the magnetic separator, thereby vibrating the entire apparatus into powder. Vibration was applied and magnetic separation processing was performed.
(Experimental conditions of Example 3)
The magnetic separator shown in FIG. 1, which is an example of the magnetic separator proposed in the present invention, has six hollow cylindrical bodies, and the vibrator installed at the bottom of the magnetic separator is vibrated to vibrate the entire apparatus into powder. Vibration was applied and magnetic separation processing was performed.

(Experimental conditions of Example 4)
The magnetic separator shown in FIG. 1, which is an example of the magnetic separator proposed in the present invention, is used in a structure in which only two hollow cylinders are left and the other hollow cylinders are removed, and the powder is not vibrated. A magnetic separation process was performed.
In conducting the experiments of Comparative Example 1 or 2 and Examples 1 to 4, the magnetic separation treatment speed, the treatment amount, and the particle size of the powder to be magnetic separation were set as follows. Table 1 shows the experimental conditions of the magnetic separation process of Comparative Example 1 or 2, and Examples 1 to 4.

(1) Powder supply rate: 30 kg / h
(2) Processing volume: 30kg
(3) Average particle size of carriers A and B and non-magnetic material C: 50 μm
The evaluation results of the magnetic classification accuracy of Comparative Example 1 or 2 and Examples 1 to 4 are shown in Table 2, and the image evaluation is shown in Table 3. In addition, these are only one aspect | mode of this invention, and this invention is not limited to these.

    Toner was mixed with carrier A and the mixed powder obtained by the magnetic separation process of Comparative Example 1 or 2 and Examples 1 to 4 at a ratio of 5 wt% to obtain a developer. In order to make it easy to evaluate the effect of the magnetic separation process, the copier is set under the condition that an abnormal image is generated even when the carrier A, which is a high magnetic material, is used, and image output is performed using the obtained developer. It was. When evaluating the image, the number of abnormal images was evaluated. Image evaluation was performed using imagio MPC3000 manufactured by Ricoh Co., Ltd.

  The magnetic separator according to the present invention can be applied to general powdery technologies such as magnetic separation of powdery substances used in various industrial fields. For example, the present invention is not limited to the field of electrophotographic carriers, and can be used as a magnetic separator for metal powder raw materials, metal powder products and the like used in various industrial fields.

It is a side conceptual diagram showing one mode of a magnetic separator concerning the present invention. It is a front conceptual diagram which shows the one aspect | mode of the magnetic separator based on this invention. It is an enlarged view of the side surface of the hollow cylindrical body and magnetic pole generating member with which the magnetic separator was equipped. It is the enlarged view which looked at the hollow cylinder from the front.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic separator exterior 2 Hollow cylinder 3 Magnetic pole generating member 4 Shaft 5 Defective product collection | recovery part 6 Input hopper 7 Input tray 9 Recovery tray 10 Powdery substance recovery hopper 13 Proximity gap of hollow cylindrical body 14 Holding part 15 Drive part 16 Vibration Child 17 Gas nozzle 20 Reticulated recess 21 Counter electrode plate

Claims (12)

A hollow cylindrical body made of at least a non-magnetic material, a magnetic pole generating member disposed inside the hollow cylindrical body, a driving unit for rotating the hollow cylindrical body, a holding unit for fixing and holding the magnetic pole generating member, A magnetic separator having a supply part for supplying a powdery substance to the surface of a hollow cylinder and a recovery part for collecting the powdery substance, comprising a plurality of the hollow cylinders, and these hollow cylinders being close to each other The magnetic separators are arranged so as to be adjacent to each other and move between the hollow cylindrical bodies arranged close to each other to reach the recovery unit. In the proximity part where the hollow cylinders are arranged close to each other, at least one part where the powdery substance moves from the hollow cylinder located below to the hollow cylinder located above is provided. The magnetic separator according to claim 1. The magnetic flux density of the magnetic field formed by the magnetic pole generating member disposed inside the hollow cylindrical body located upstream of the movement path of the powdery substance at the proximity portion where the hollow cylindrical body is disposed in proximity. When B1 [T] and B2 [T], the magnetic flux density of the magnetic field formed by the magnetic pole generating member disposed inside the hollow cylindrical body located on the downstream side of the movement path of the powdery substance is 0 The magnetic separator according to claim 1, wherein a condition of ≦ Log (B2 / B1) ≦ 5 is satisfied. The magnetic separator according to any one of claims 1 to 3, wherein the powdery substance is vibrated by applying vibration to the hollow cylindrical body. The magnetic separator according to any one of claims 1 to 3, wherein the powdery substance is vibrated by blowing a gas onto the powdery substance moving on the surface of the hollow cylindrical body. The counter electrode plate is provided close to the hollow cylindrical body, and the powdered substance is vibrated by applying an AC voltage between the hollow cylindrical body and the counter electrode plate. Magnetic separator according to 1. The magnetic separator according to any one of claims 1 to 6, wherein the adjacent interval between the adjacent hollow cylindrical bodies is 3 mm to 50 mm. The magnetic separator according to any one of claims 1 to 7, wherein at least a part of the surface of the hollow cylindrical body has an uneven shape. The magnetic separator according to any one of claims 1 to 8, wherein one hollow cylinder rotates in a clockwise direction and another adjacent hollow cylinder rotates in a counterclockwise direction. The average value of the rotational speed of each of the plurality of hollow cylinders is R [rpm], the radius of the hollow cylinder is r [cm], and the supply speed of the powdery substance supplied to any surface of the hollow cylinder is The magnetic separator according to any one of claims 1 to 9, wherein when M [kg / h] is satisfied, a condition of 2 ≦ 1000 (M / 2πrR) ≦ 80 is satisfied. The magnetic separator according to any one of claims 1 to 10, wherein the powdery substance is an electrophotographic carrier. An electrophotographic carrier that is magnetically selected by the magnetic separator according to claim 11.